Reflection of Sound Signals in the Troposphere

Experiments directed toward the detection of non-homogeneities in the first few hundred feet of the atmosphere were carried out with a low power sonic “radar.” The device has been named the sodar. Trains of audiofrequency sound waves were launched vertically upward from the ground, and echoes of sufficient magnitude to be displayed on an oscilloscope were found. Strong displays tended to accompany strong temperature inversions. During these periods, transmission on a microwave radio path along which the sodar was located tended to be disturbed by fading. In addition, relatively strong echoes were received when the atmosphere was in a state of considerable turbulence. There was a well-defined fine-weather diurnal characteristic. The strength of the echoes was such as to lead to the conclusion that a more complicated distribution of boundaries than those measured by ordinary meteorological methods is required in the physical picture of the lower troposphere.